U.S. Pat. No. 2,198,822 describes certain amphoteric shampoo materials including products of the formula: ##STR1## wherein R is a hydrocarbon radical of 6-24 carbon atoms, Y is aliphatic hydrocarbon of 1-6 carbons or -R.sup.1 -O (R.sup.1 O).sub.x H wherein R.sup.1 is alkylene of 2-4 carbons and x is 0-15 and M is hydrogen, sodium, potassium or other alkali metal.
These products are not stated to have any stability in strong alkali. Also, U.S. Pat. No. 2,168,538 describes certain amide derivatives of the general formula: ##STR2## wherein R is hydrocarbon of 4 to 18 carbon atoms, R.sup.3 is alkylene of 2 to 4 carbons, R.sup.2 is alkylene or hydroxy alkylene of 2 to 6 carbon atoms or an alkylene oxide adduct thereof and R.sup.1 is hydrogen, alkyl, hydroxy alkyl or an alkylene oxide adduct thereof, M is hydrogen or an alkali metal. Reference is made to possible quaternized oligomers of these compounds but there is no exemplification of such products.
These products also are not stated to possess any special stability toward alkali.
U.S. Pat. No. 4,246,194 (Ferguson assigned to Research Organics Inc. issued January 20, I98l) discloses compounds inter alia of the formula: ##STR3## wherein A and B are each hydrogen, aliphatic, cycloaliphatic or hydroxyaliphatic and n is 1 or 2. The compounds are stated to be useful as hydrogen ion buffers in a desirable pKa range for biological research. No suggestion is made that the products should be quaternized. Nor is there any suggestion that quaternized products would be useful.
The need for surface active agents that are stable in moderately strong alkali is discussed in U.S. Pat. No. 4,214,102. This patent teaches that the presence of an amide linkage destablizes many materials in strong acids and strong alkalies since this linkage readily breaks down in such media resulting in turbid solutions. The objective of the invention described therein is said to be "the development of amphoteric surface-active compounds which are stable over a wide pH range from acidic to alkaline over long periods of time and which have at least three hydroxyl and/or ether groups to give a greater hydrophilic effect to the molecule". The products are obtained by reaction of a glycidyl ether with an excess of an N-hydroxy-C.sub.2-4 -alkyl-C.sub.2-6 -alkylene diamine and then N-alkylating the product with an excess of halo C.sub.2-4 alkanoic acid or halo C.sub.2-4 hydroxyalkane sulfonic acid. Among the compounds produced are ones that have "the probable formulae": ##STR4##
The products formed are shown to be good foamers and stable in either 20% NaOH or 20% H.sub.2 SO.sub.4. However, the surface tension of 20% NaOH containing either 1% or 5% of the subject product was only reduced to 66.4 dyne/cm indicating very poor surface activity in such a solution.
Alkylamino sulfonic acids are also described in U.S. Pat. Nos. 4,481,150; 4,138,345; 3,998,796; 3,075,899;and 1,994,300. None of these claim any particular alkali stability for the products disclosed.
Zielinska (Chemical Abstracts 104:209 195 c describes surfactants of the formula EQU ROCH.sub.2 CH(OH)CH.sub.2 N.sym.R'.sub.2 CH.sub.2 CH(OH)CH.sub.2 SO.crclbar..sub.3
that are prepared by reaction of compounds of the formula EQU ROCH.sub.2 CH(OH)CH.sub.2 NR'.sub.2 or RNHCH.sub.2 CH.sub.2 NR'.sub.2
with epichlorohydrin and sodium sulfite. They are stated to have good detergent and bactericidal properties.
There has long been a need for alkali-stable surface active agents. The only product currently on the market that is stable in concentrated alkali (30-50% solutions of NaOH) is that sold under the trademark Triton BG-10. This product is comprised of higher alkyl monosaccharides and higher alkyl oligosaccharides of the type described in U.S. Pat. No. 3,839,318. Triton BG-10 has several shortcomings: it is quite dark, viscous, has a burnt odor, only slowly dissolves in 50% NaOH, does not reduce the surface tension of 50% NaOH to any great extent, and produces considerable foam as well.
It is an object of the present invention to produce materials that are compatible with aqueous solutions of NaOH containing up to 50% NaOH. It is a further object of this invention to produce materials that dissolve readily in concentrated aqueous NaOH and that appreciably reduce the surface tension of such solutions. A further object is to produce materials that will remain dissolved when concentrated NaOH containing these materials is diluted with water to normal use concentrations of 5-20% NaOH and will significantly lower the surface tension of such solutions. A further object is to produce materials that will generate little or no foam in solutions containing 50% or less NaOH. Still a further object of the present invention is to produce materials that will remain unchanged in solutions containing 5-20% NaOH upon extended boiling of such solutions.
These and other objects are achieved by use of materials of the general formula: ##STR5## wherein R is selected from alkyl, aryl, or alkylaryl groups of 4-18 carbon atoms or alkoxymethylene wherein the alkoxy group contains 4-18 carbon atoms. R.sup.2 and R.sup.3 are individually selected from the group consisting of methyl; alkyl of 2-6 carbon atoms, where said alkyl group is substituted by an electron-donating group on the beta carbon atom thereof; polyoxyethylene and polyoxypropylene. Alternatively, R.sup.2 and R.sup.3 may together be --CH.sub.2 CH.sub.2 OCH.sub.2 CH.sub.2 -- or --CH.sub.2 CH.sub.2 SCH.sub.2 CH.sub.2 -- (i.e. together with nitrogen constitute a morpholine or thiomorpholine ring).
M is hydrogen or an alkali metal cation; and X is hydrogen or an electron-donating group such as OH, SH, CH.sub.3 O or CH.sub.3 S.
Typically the R group contains 4-14, commonly 4-8 carbon atoms. Preferably, R is alkoxymethylene containing 4-8 carbon atoms in the alkoxy group such as butoxymethylene, hexyloxymethylene, 2-ethylhexyloxymethylene. R.sup.2 and R.sup.3 are each preferably methyl, hydroxyethyl, 2-hydroxypropyl, or together, and with the nitrogen atom to which they are bound, form a morpholine ring. X is preferably hydrogen.
Without wishing to be bound by any theory, it is believed that the alkali stability of the products of the present invention derives from the general provision of electron-donating groups on carbon atoms in positions beta to quaternary nitrogen. Such groups make the hydrogens of beta carbon atoms less acidic and thereby counteract degradative processes such as those described by Hofmann (Ber., 14, 659 (1881). Typically such groups include hydroxy, alkoxy, mercapto, and alkylthio. Suitable alkoxy and alklythio groups contain 1-4 carbon atoms.
The products of the present invention are prepared by alkylation of a compound of the formula: ##STR6## with an alkylating agent of the formula: ##STR7## where Hal is halogen, typically chlorine and M is an alkali metal cation, typically sodium.